logb-Radix-independent Exponent

F_TYPE logb (F_TYPE x)

logb() returns a signed integer converted to double-precision floating-point and so chosen that 1 <= |x|/2**n < 2 unless x = 0 or |x| = infinity.

IEEE Std 754 defines logb(+infinity) = +infinity and logb(0) = - infinity. The latter is required to signal division by zero.

Exceptional Argument       Routine Behavior

|x| = infinity             Invalid argument